Induction heating type fusing device and image forming apparatus employing the same

Abstract

An induction heating type fusing device and an image forming apparatus including the fusing device. The fusing device includes a magnetic flux generator and a compressing roller outside a fusing belt, first and second fusing rollers and a nip guide inside the fusing belt. The compressing roller compresses against the first and second fusing rollers and the nip guide to form nips, while the fusing belt is disposed between the compressing roller and the first and second fusing rollers and the nip guide.

What is claimed is: 
     
       1. A fusing device comprising:
 a fusing belt formed as a closed loop; 
 a magnetic flux generator disposed outside the fusing belt to emit magnetic flux for induction heating of the fusing belt; 
 a first fusing roller and a second fusing roller that are disposed in parallel with each other inside the fusing belt and support the fusing belt; 
 a nip guide located between the first fusing roller and the second fusing roller; and 
 a compressing roller disposed on an outer portion of the fusing belt for compressing against the first and second fusing rollers and the nip guide to form nips on portions of the fusing belt, 
 wherein the magnetic flux generator includes a coil wound along a length direction of the first and second fusing rollers, and a cross-section of the coil is curved along an outer circumference of the fusing belt with respect to the first fusing roller and with respect to the second fusing roller. 
 
     
     
       2. The fusing device of  claim 1 , wherein the magnetic flux generator further comprises:
 a magnetic core disposed to face the fusing belt while the coil is disposed between the magnetic core and the fusing belt to guide magnetic flux generated by the coil; and 
 a bobbin supporting the coil and the magnetic core. 
 
     
     
       3. The fusing device of  claim 2 , wherein a distance between the coil and the fusing belt is maintained constant. 
     
     
       4. The fusing device of  claim 2 , wherein the magnetic core comprises:
 a main core including a plurality of core pieces that are arranged in the length direction of the first and second fusing rollers; and 
 two end cores extending in the length direction of the first and second fusing rollers and contacting ends of the plurality of core pieces. 
 
     
     
       5. The fusing device of  claim 4 , wherein each of the plurality of core pieces has an arch-shaped cross-section. 
     
     
       6. The fusing device of  claim 4 , wherein core pieces located at ends among the plurality of core pieces have an E-shaped cross-section having a protruding center portion. 
     
     
       7. The fusing device of  claim 4 , wherein core pieces located at ends among the plurality of core pieces have a core body having an arch-shaped cross-section and a center core having a first side contacting a center portion of the core body and a second side located inside the coil. 
     
     
       8. The fusing device of  claim 1 , wherein the fusing belt comprises a release layer and a heating layer. 
     
     
       9. The fusing device of  claim 8 , wherein the fusing belt further comprises an elastic layer. 
     
     
       10. The fusing device of  claim 9 , wherein the release layer is an outer layer of the fusing belt, the heating layer is an inner layer of the fusing belt, and the elastic layer is disposed therebetween. 
     
     
       11. The fusing device of  claim 8 , wherein the heating layer is formed of a conductive magnetic material. 
     
     
       12. The fusing device of  claim 1 , wherein each of the first and second fusing rollers comprises a supporting layer and a heat insulating layer surrounding the supporting layer. 
     
     
       13. The fusing device of  claim 1 , wherein the nip guide comprises an elastic layer and a supporting layer supporting the elastic layer. 
     
     
       14. The fusing device of  claim 1 , wherein the compressing roller comprises a release layer, an elastic layer, and a supporting layer. 
     
     
       15. The fusing device of  claim 14 , wherein the supporting layer of the compressing roller is a hollow shaft or a rod. 
     
     
       16. The fusing device of  claim 1 , further comprising a second heat source disposed inside the compressing roller. 
     
     
       17. The fusing device of  claim 16 , wherein the second heat source is a halogen lamp. 
     
     
       18. The fusing device of  claim 1 , further comprising a second heat source disposed outside of the compressing roller. 
     
     
       19. The fusing device of  claim 18 , wherein the second heat source is a halogen lamp and a thin pipe surrounding the halogen lamp. 
     
     
       20. An image forming apparatus comprising:
 electrophotographic type printing units for transferring toner images onto a printing medium; and 
 a fusing device for fusing the transferred toner images on the printing medium, 
 wherein the fusing device includes: 
 a fusing belt formed as a closed loop; 
 a magnetic flux generator disposed outside the fusing belt to emit magnetic flux for induction heating of the fusing belt; 
 a first fusing roller and a second fusing roller that are disposed in parallel with each other inside the fusing belt and support the fusing belt; 
 a nip guide located between the first fusing roller and the second fusing roller; and 
 a compressing roller disposed on an outer portion of the fusing belt for compressing against the first and second fusing rollers and the nip guide to form nips on portions of the fusing belt, 
 wherein the magnetic flux generator includes a coil wound along a length direction of the first and second fusing rollers, and a cross-section of the coil is curved along an outer circumference of the fusing belt with respect to the first fusing roller and with respect to the second fusing roller. 
 
     
     
       21. The image forming apparatus of  claim 20 , wherein the magnetic flux generator further comprises:
 a magnetic core disposed to face the fusing belt while the coil is disposed between the magnetic core and the fusing belt to guide magnetic flux generated by the coil; and 
 a bobbin supporting the coil and the magnetic core. 
 
     
     
       22. The image forming apparatus of  claim 21 , wherein a distance between the coil and the fusing belt is maintained constant. 
     
     
       23. The image forming apparatus of  claim 21 , wherein the magnetic core comprises:
 a main core including a plurality of core pieces that are arranged in the length direction of the first and second fusing rollers; and 
 two end cores extending in the length direction of the first and second fusing rollers and contacting ends of the plurality of core pieces. 
 
     
     
       24. The image forming apparatus of  claim 20 , wherein the fusing belt comprises a release layer and a heating layer. 
     
     
       25. The image forming apparatus of  claim 24 , wherein the fusing belt further comprises an elastic layer. 
     
     
       26. The image forming apparatus of  claim 20 , wherein each of the first and second fusing rollers comprises a supporting layer and a heat insulating layer surrounding the supporting layer. 
     
     
       27. The image forming apparatus of  claim 20 , wherein the nip guide comprises an elastic layer and a supporting layer supporting the elastic layer. 
     
     
       28. The image forming apparatus of  claim 20 , wherein the compressing roller comprises a release layer, an elastic layer, and a supporting layer. 
     
     
       29. The image forming apparatus of  claim 20 , further comprising a second heat source disposed inside the compressing roller. 
     
     
       30. The image forming apparatus of  claim 20 , further comprising a second heat source disposed outside of the compressing roller.